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SOLID-HOOFED PIGS

of these, and that which has given its name to the group,
concerns the arrangement of the digits. Instead of there being
but one prevailing digit—the third, in the hand and foot,
through which the axis of the foot passes, there are two, numbers
three and four, between which the same axis passes, and which
are perfectly symmetrical with each other. This type of foot has
been termed " paraxonic," as opposed to the " mesaxonic " Perisso-
dactyle foot (see Fig. 121 B, p. 235). It has been attempted
to prove that the single prevailing digit of the Horse's foot is a
fused pair of digits, and the state of affairs which characterises
the Camel, where the two metacarpals or metatarsals are to an
almost complete extent united, has been urged in proof; so,
too, certain abnormalities, such as those called " solid-hoofed
pigs." 1 These latter are simply Pigs in which the two central
metacarpals and the terminal hoofs are completely fused with one
another. In some of such cases there is not the slightest trace of
the union of the separate metacarpals and phalanges. Even the
sesamoid bones, attached behind to the toes, are two in number
instead of four. And, furthermore, the tendon supplying the
bones is single, though showing traces of its double origin.
Such Pigs often show the abnormality from generation to genera-
tion, and they proved convenient for those whose scruples would
not allow them to eat the flesh of a beast " dividing the hoof **
and not chewing the cud. More singular still, as showing a
pathological approach from another side to the Perissodactyle
condition in an Artiodactyle, is a calf, where the foot ended in
three equi-sized digits, of which the middle one lay in the longi-
tudinal axis of the limb. From the opposite, side cases are
known of a Horse with a split hoof and phalanges, thus present-
ing the most striking likeness to a Camel.
There is, furthermore, in certain groups of Artiodactyles
(e.g. the Tragulidae) a tendency for the two middle mefcacarpals to
unite, quite apart from such " sports *' as thoise illustrated by the
cases just set forth. And, as already mentioned, the union of the
two middle metacarpals culminates in the Camel, Ox, etc. There
is, however, absolutely no trace of such a fusion in the series of
Perissodactyle animals known to us; and it would be by fusion
rather than dismemberment that, as it would appear on this
theory, the modern Ungulate foot has been arrived at. Of course
•' See Batesoa, Materials for the Study of Farw^w, London, 1894, p. 387,